Drinking two cups of hot chocolate a day may boost memory in pensioners by almost a third.

It is thought chocolate’s ability to boost blood circulation is the reason.

Drinking just two cups of hot chocolate a day helps elderly people keep their brains healthy and their minds sharp by boosting the blood flow to their brains

'We're learning more about blood flow in the brain and its effect on thinking skills,' said lead author Dr Farzaneh Sorond, from Harvard Medical School.

'As different areas of the brain need more energy to complete their tasks, they also need greater blood flow. This relationship, called neurovascular coupling, may play an important role in diseases such as Alzheimer's.'

The study, published in the journal Neurology, involved 60 people with an average age of 73 who did not have dementia.

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Each volunteer drank two cups of hot cocoa a day for a month and did not consume any other chocolate during the study.

Both their memory and thinking skills were examined, while they also had ultrasounds to measure the blood flow to the brain during the tests.

Almost a third of participants had impaired blood flow at the start of the study, but saw an 8.3-per cent improvement in flow to the working areas of the brain by the end of the study.

Drinking hot chocolate can reduce a person's risk of dementia by increasing the blood flow to their brain by up to eight per cent

This group with impaired blood flow also experienced improved times after taking a test of working memory, with scores falling from 167 to 116 seconds by the end of the month.

In both instances, there was no improvement for those who started out with regular blood flow.

Half of the study participants received hot cocoa that was rich in the antioxidant flavanol, while the other half received flavanol-poor hot cocoa. There were no differences between the two groups in the results.

The beneficial effects on the brain have been shown only for dark chocolate which is at least 60-70 per cent cocoa

'More work is needed to prove a link between cocoa, blood flow problems and cognitive decline,' said Dr Paul Rosenberg, from Johns Hopkins School of Medicine. 'But this is an important first step that could guide future studies.'

Previous research has found that lovers of dark chocolate - with at least 60-70 per cent cocoa - benefit from a protective effect against high blood pressure and the risk of diabetes.

And scientists say it can even benefit those who are already at high risk of heart attacks and strokes.

The beneficial effects have been shown only for dark chocolate which is at least 60-70 per cent cocoa. Milk or white chocolate does not provide the same benefits.

It is rich in flavonoids which are known to have heart protecting effects. Sceptics say the high calorie content of chocolate tends to offset the benefits.

Another study found that eating chocolate reduces blood pressure and improves insulin sensitivity, reducing the risk of diabetes.

Dr Simon Ridley, head of research at Alzheimer's Research UK, said: 'This small study adds to a wealth of existing evidence linking vascular problems and poorer cognition. A cocoa-based treatment would likely be very popular, but it's too soon to draw any conclusions about its effects.

'Dementia is one of the greatest medical challenges we face today, and it's vital that we invest in research to find ways to prevent the condition.

‘Poor vascular health is a known risk factor for dementia, and understanding more about the links between vascular problems and declining brain health could help the search for new treatments and preventions.'